A process for obtaining security paper, in particular paper money

Abstract: Starting with the classic incorporation to the security paper of security threads or strips (1) carrying a drawing (2) or any mark that can be readily detected with the naked eye, obtained upon a metallised background (3), the process comprises rendering the said metallised background (3) discontinuous, to define a sort of screen or the like, that reduces the intensity of the background and renders the latter more difficult to reproduce by optical means and at the same time allowing the said drawing (2) to be printed using cheaper and more accessible techniques. Furthermore, the discontinuous character of the metallised background (3) allows fluorescences to be used on either the screen dots (3) upon non-fluorescent background material or upon fluorescent background material having a colour that differs from that of the screen fluorescence.

Description: OBJECT OF THE INVENTION The present invention relates to a security paper containing a security strip or thread applicable in particular to paper money, which paper is aimed at achieving a greater security, i.e. making reproduction more difficult, and at the same time achieving greater savings in the process for obtaining the same. BACKGROUND OF THE INVENTION As is well known, in manufacturing paper money and other kinds of security paper, the use of security threads or strips made of a transparent film having a layer of reflective metal, such as vacuum deposited aluminium on a sheet of polyester, is absolutely widespread, the said strips or threads being embedded in the security paper as such, the latter then undergoing the inevitable printing stage. This yields a security document, for instance a banknote, in which the security threads are barely visible under reflected light and yet stand out immediately and substantially when the document is observed under transmitted light, because of the darkness of the security thread. Though this is a very effective solution, it is possible to enhance the level of security of the paper by providing the security strip or thread with a drawing that the public may readily recognise, whilst retaining the aforesaid optical variation effect. This is feasible by various means, for instance by vacuum depositing aluminium through a mask, selectively eliminating aluminium from a strip comprising a mixture of a plastic base and aluminium using an excimer laser, and so forth. The characters printed on the thread or band ore however sometimes too small to be recognised by merely observing the document, and if their size is increased the printed characters shall stand out overmuch when viewed under a reflected light, whence they will be easily copied by a counterfeiter. In an attempt at overcoming this problem European patent 0 319 157 A is known to allow the use of a drawing having characters that are sufficiently large to be visible with the naked eye, obtained using a partially metallised strip, thereby essentially maintaining the strong optical variation impact of a continuous metallised strip. This effect is in particular achieved using & waterproof and flexible substrate, with a layer of metal on either side thereof, with a continuous metallic sector lengthwise on one of its sides having non-metallic areas that take up between 10 and 50% of the surface and obtained using a stencil, design or reiterative drawing, at least part of the transverse non-metallic areas being wholly surrounded with metal. DESCRIPTION OF THE INVENTION The security paper subject of the present invention is firstly designed to improve the reliability of the document, thereof implying a higher difficulty of reproducing the same, and on the other providing greater savings or a cost reduction during production, without this impairing security. More specifically and in order to achieve the above, using the same basic conventional idea of providing the security thread with a drawing that the public may readily recognise, the invention focusses on establishing a discontinuous background metallisation or print, in particular using a screen or the like, in such a way that the background is not so dearly visible and may prove more difficult to reproduce by optical means, which background can further be obtained by means of current printing techniques such as mezzotint, that are far more accessible for the manufacturer than continuous metallisation techniques, which are also much slower. Screen printing further allows an easy incorporation in the paper, in particular to the security thread, of a fluorescent element, which is extremely difficult when the dark portion is continuous, i.e. when the said metallisation is continuous. With the process of the invention it is possible for the fluorescence to be provided on the screen dots and for the background material to be non-fluorescent, or for the background material be a different colour fluorescent material as regards the screen fluorescence, thereby to achieve a more noticeable effect. DESCRIPTION OF THE DRAWINGS In order to provide a fuller description and contribute to complete understanding of the characteristics of this invention, a single sheet of drawings is attached to the specification which, while purely illustrative and not fully comprehensive, shows in its only figure a security thread in accordance with the process for obtaining security paper, and in particular in accordance with the improvements of such process, that are the object of the present invention. PREFERRED EMBODIMENT OF THE INVENTION The said figure shows that the security thread (1), that can optionally be a strip or a band, is provided with an opaque background for the letters or drawings (2) that shall constitute the distinguishing feature to be recognised by the public, namely a discontinuous metallisation (3), as a screen, which, being of a discontinuous character, causes the opaque background to be less intensively opaque than a continuous metallised background which as aforesaid means that it is on the one hand more difficult to reproduce by optical means and on the other allows the same to be manufactured using printing techniques that are cheaper and hence far more accessible for security paper manufacturers than continuous metallised background techniques, that in addition to being more costly have a slower and hence more expensive process. Now therefore, reproduction is with the security paper of the invention on the one hand more difficult and on the other much cheaper to carry out, without security being impaired, inasmuch as since a security provided within the actual security paper, i.e. inside the same, such is guaranteed for the said paper normally carries a watermark, fibril and other security elements preventing any implantation inside the same. Furthermore and as aforesaid, the discontinuous screen or metallisation provided for the security paper of the invention allows a fluorescent element to be easily incorporated to the paper, and moreover in a twofold manner, with the fluorescence on the screen dots and the background material being non-fluorescent, or with the background material being fluorescent and having a colour that is distinct from the screen fluorescence. It is also possible for the printed parts to be separated by areas where the fluorescent element can be enhanced, i.e. in the area where the microprint would be provided on a dark screen background the screen colour would prevail, which could for instance be black, in the areas between the printed letters or drawings there would be no screen and the background would prevail, and the in the said background the fluorescence could be enhanced.

Claims: A security paper containing a strip or thread (1), applicable in particular to paper money, said security strip or thread being included within the paper and said strip or thread carrying letters or drawings (2) on a coated base running along the strip or thread such that a viewer may easily recognise said letters or drawings, characterised in that said coated base being discontinuous and consisting of metallic or dark coloured printed dots defining a screen which delimits the outline of the letters or drawings and which renders said discontinuous coated base less strong; and in that said security strip or thread optionally includes fluorescent elements. A security paper containing a security strip or thread applicable, in particular to paper money, according to claim 1, characterised in that the fluorescent elements are located on the screen dots upon a non fluorescent base material. A security paper containing a security strip or thread, in particular to paper money, according to claim 1, characterised in that the fluorescent elements are located on the screen dots upon fluorescent base material, both fluorescences being distinguishable by being of different colours.

Inventors: TEODORO VIDAL JUAN, TEODORO, VIDAL, JUAN
Applicants: NAC DE MONEDA Y TIMBRE FAB, FABRICA NACIONAL DE MONEDA Y TIMBRE
Application year: 1994
Main classification: B41M3
IPC codes: B42D15, G03C5, B41M3, D21H21